Field of the Invention
The present disclosure relates to a method and system for linearizing the performance of amplifiers using transistor-level dynamic feedback.
Description of the Related Art
Amplifiers are often treated as linear devices that amplify an input signal via a constant gain factor. It is well understood in the art that amplifiers often possess nonlinear performance above a certain threshold of input power. For example, as the power level of an input signal increases above such a threshold, an amplifier's ability to provide gain will often increasingly degrade. This can result in a distorted output signal from the amplifier due to the low-power elements of the input signal having been amplified with a higher gain factor than the high-power elements of the input signal.
One solution to avoiding nonlinear performance in an amplifier is to restrict input signals to below the threshold where such signals would induce nonlinear distortions. However, this may be undesirable as such a restriction limits the power efficiency that can be obtained when using such an amplifier.
Another approach in the prior art is to use a pre-distortion circuit prior to the amplifier to correct for the nonlinear distortions of the amplifier. For example, if a non-linear amplifier has a gain profile characterized by the function y=√{square root over (x)}, then using a pre-distortion circuit prior to the amplifier with a gain profile characterized by the function y=x2 should result in linear performance (i.e., y=x). The problem with this approach is that it often creates unwanted intermodulation distortion byproducts that arise from small but significant mismatches between the pre-distortion circuit and the nonlinear profile of the amplifier. Such mismatches often occur for a variety of reason, such as the pre-distortion circuit and the amplifier being influenced by environmental factors (e.g., temperature, humidity, or supply voltage fluctuations) or the slow degradation of these devices over time. Another problem with pre-distortion circuits is that they typically consume considerable power. In addition, they often require highly complex and costly designs as they must operate at often very high frequencies and also provide a very high operating bandwidth so that intermodulation distortion byproducts can be canceled out within the amplifier.